Seismic expansion joint covers for buildings in geographic regions that are prone to earthquakes are of special designs that allow for movements of the building units on either side of the expansion gap that are very much greater than the movements that occur as a result of thermal expansion and contraction. In that regard, buildings currently being built in earthquake-prone regions are usually supported on isolators that attenuate the intensities of shocks imparted to the building structure but increase the durations and magnitudes of the swaying motions of the structure as the structure displaces and deforms when forces due to the earthquake are imposed on its foundation supports. When a building is composed of two or more adjacent independent structural units, each structural unit is subject to movements in an earthquake that are different in direction, frequency and magnitude. That is the case, indeed, regardless of whether the units are mounted on isolators or not.
Adjacent structural units of a building are, in particular, subject to large relative movements having components horizontally toward and away from each other (perpendicular to the gap)xe2x80x94x-axis movementsxe2x80x94and components horizontally parallel to the gapxe2x80x94y-axis movements. Because the connections between structural units at expansion joints (which might better be termed xe2x80x9cmotion-absorbing gapsxe2x80x9d) occur at the perimeters of the structural units, the movements include small but meaningful relative displacements vertically and angularly between portions on opposite sides of gaps due to the rocking of the floors at the perimeter of the structural unit about a fulcrum in the region of the bottom center of the structural unit.
U.S. Pat. No. 5,644,879 (Shreiner et al., Jul. 8, 1997), which is owned by the assignee of the present invention and is hereby incorporated herein by reference for all purposes, describes and shows a seismic expansion joint cover assembly that is adapted to span a gap between the floors of building sections on opposite sides of a motion-absorbing gap and that permits relative movements of the floors substantially horizontally toward and away from each other along an axis perpendicular to the gap (xe2x80x9cx-axis directionxe2x80x9d) and substantially horizontally relative to each other along an axis parallel to the gap (xe2x80x9cy-axis directionxe2x80x9d). The assembly includes a rectangular structural floor bridge panel that spans the gap in all relative positions of the floors. One end of the bridge panel is attached to the floor on one side of the gap (xe2x80x9cfloor Axe2x80x9d) for movement in the y-axis direction and against movement in the x-axis direction relative to floor A. The other end of the bridge panel is supported on the floor of the other building section (xe2x80x9cfloor Bxe2x80x9d) for movement in the x-axis direction and against movement in the y-axis direction relative to floor B.
U.S. Pat. No. 5,666,775 (Shreiner et al., Sep. 16, 1997), which is also owned by the assignee of the present invention and is also hereby incorporated herein by reference for all purposes, describes and shows a wall expansion joint cover that is secured to the wall members on opposite sides of an expansion gap by hook and loop fasteners and is tethered to the wall by cords so that it is prevented from falling to the floor and becoming a safety hazard by impeding passage of persons across the gap during and after an earthquake dislodges it. U. S. Pat. No. 5,794,456 (Shreiner et al., Sept. 1, 1998), another patent owned by the assignee of the present invention (and hereby incorporated herein by reference for all purposes), discloses elastic cords for keeping a wall expansion joint cover centered in a motion-absorbing gap.
Both wall expansion joint covers (interior and exterior) and ceiling expansion joint covers are subject to conditions that differ somewhat from those of floor expansion joint covers. In the case of walls, the cover panel that extends across and covers the motion-absorbing gap lies vertically. Therefore, the cover panel has to be configured and installed in a manner that allows relative movements of structural units of the building perpendicular to the plane of the cover of much greater magnitudes than those of floor expansion joint covers. Exterior wall expansion joint covers are subject to high wind loads acting both toward and away from the building wall on which they are installed. Floor expansion joint covers are subject only to downward vertical loads (due to persons and objects moving across them)xe2x80x94gravity holds them down. The covers of wall expansion joint covers that are dislodged in whole or in part from the expansion gap do not return automatically to their installed positions after dislodgment by an earthquake. Floor expansion joint covers usually reseat automatically when an earthquake ceases. Although reseating of interior expansion joint covers is not difficult, because they are generally accessible to workers from within the building, immediate reseating of interior wall expansion joint covers to close the relatively large motion-absorbing gap is important to the safety of persons that occupy the building after an earthquake. Reseating of exterior wall expansion joint covers above the ground floor, though not required immediately except possibly in bad weather to prevent intrusion of rain or snow, requires workers to climb ladders or be lowered on cable-supported work platforms to gain access to the wall covers.
Ceiling expansion joint covers are subject to the same relative motions as floor expansion joint covers. Whereas floor expansion joint covers are essentially self-seating by gravity, ceiling expansion joint covers must be fastened against gravity. Like wall expansion joint covers, ceiling expansion joint covers can be reseated from within the building. It is desirable, however, for convenience and safety that they not be permitted to move appreciably away from the plane of the ceiling when they are dislodged in an earthquake.
Although the expansion joint covers disclosed in the aforementioned patents and various other previously known expansion joint covers meet the requirements imposed on them reasonably well, there is a need for wall and ceiling expansion joint covers that are relatively simple in construction and function, relatively inexpensive to produce and install, capable of reseating automatically after the end of an earthquake that dislodges them, and versatile as far as utility in various environments is concerned. Further desirable objectives that are not fully met by many previously known wall and ceiling expansion joint covers include light weight cover panels, which minimizes dynamic loads exerted on various parts of the expansion joint cover system, and reliable, long-lived functional elements, which resist damage and enable a long service life of an installation without repair or replacement.
The foregoing needs and objectives are met, in accordance with the present invention, by a seismic expansion joint cover assembly installed at a motion-absorbing gap between a member A on one side of the gap and a member B on the other side of the gap. The assembly includes a cover panel spanning the gap and a hinge joining one edge A of the cover panel to the member A for pivotal movement about a pivot axis. The pivot axis is spaced apart from the expansion gap so as to enable a stop between the cover panel and member A to prevent the cover panel from pivoting about the pivot axis into the expansion gap upon widening of the expansion gap. A permanent magnet and magnet striker releasably secure the other edge B of the cover panel to the member B.
The hinged connection of the end A of the cover panel to the member A leaves the end B free to swing out a considerable distance when member B moves relative to member A such as to engage the cover panel and to release the magnetic connection. That aspect of the invention is especially useful for interior and exterior wall covers, in which the cover panels are vertical and the members A and B displace relative to one another horizontally in directions parallel to the center plane of the expansion gap. The location of the pivot axis in spaced-apart relation from the gap and a stop on member A prevents the cover panel from moving into the gap when the gap widens. The magnetic latching of the cover panel to the member B holds the cover panel closed under normal (no earthquake) conditions, is relatively inexpensive and reliable, and allows the member B to move relative to member A by sliding of the magnet relative to the striker upon small movements of members A and B due to thermal expansion/contraction of the building units of which members A and B are parts.
In order to best use available space and keep the cover panel light in weight, it is preferable that the magnet be mounted on the member B and the magnet striker be mounted on the cover panel.
Preferred embodiments of the present invention incorporate a biasing system connected to the cover panel at a location spaced apart from the pivot axis and connected to one of the members A and B for continuously biasing the cover panel about the pivot axis toward a covering relation to the expansion gap with the permanent magnet and magnet striker engaged. A biasing system restricts the extent of the of pivotal movement of the cover panel away from the closed position in an earthquake and recloses the cover panel after an earthquake. Reclosing of the cover panel on an interior wall and a ceiling is highly desirable for the safety of persons who pass across the motion-absorbing gap. Automatic reclosing of the cover panel on an exterior wall by a biasing system makes it unnecessary for workers to manually reclose the cover panel and provides immediate reclosing for weather protection.
One suitable biasing unit includes a weight and a flexible strand, such as a rope or wire cable. The strand is connected at one end to the cover panel, is trained over a guide secured to one of the members A and B, runs from the guide to the weight, and is joined at the other end to the weight. The weight is freely supported vertically by a segment of the strand running from the guide to the weight. Although a biasing unit based on a suspended weight can be used in installations on interior walls and ceilings, it has the particular advantage in an exterior wall cover installation of readily providing a strong and constant closing force, which not only ensures closing of the cover panel against wind loads but provides a force supplementing the magnet latch to hold the cover panel closed against wind loads that can create a pressure difference between the inside and outside of the cover panel when the cover panel is on the downwind side of the building. It is desirable for the weight to be slidably received in a guide tube that prevents the weight from swinging in an earthquake while permitting the weight to move vertically. The guide tube may be mounted on member B in a recess adjacent the corner of the gap. The magnet can also be mounted in the recess.
Uncontrolled rebounding or xe2x80x9choppingxe2x80x9d of the weight can produce high loads on all elements of a biasing system having a weight. In preferred embodiments of weight-based biasing arrangements according to the present invention, an anti-rebound shock cord is connected between the weight and a fixed point substantially vertically below the weight (at the lowest point of the weight). The anti-rebound shock cord arrests upward movements of the weight at all positions of the weight. For example, when the cover panel stops moving from closed to open, the anti-rebound shock cord retards the continued upward movement of the weight due to its inertia and supplements the gravity force on the weight in moving the weight down. The force of the anti-rebound shock cord is also an element of the total closing force applied to the cover panel.
Another suitable biasing unit includes an elastic member, such as a length of xe2x80x9cshock cord,xe2x80x9d connected under tension between the cover panel and one of the members A and B. An elastic member is relatively inexpensive and easy to install. An elastic member can be connected at its ends to the cover panel at spaced-apart locations axially of and within the gap and hooked for free running intermediate the ends to one of the members A and B. The free-running of the intermediate connection through a hook provides substantially equal tension forces between the hook and the ends.
In preferred embodiments, the cover panel includes a skeletal frame, aluminum members being desirable for low weight, and a facing member secured to the frame. The facing member may, for example, be a sheet of a metal or a composite material.
For good appearance of the cover installation, member A and member B may have recesses adjacent the gap that receive edge portions of the cover panel so that the exterior surfaces of the cover panel are flush with surfaces of the members A and B adjacent the recesses. In a recessed installation, a frame member is provided at the edge of the recess of member B remote from the expansion gap, the frame member having a cam surface sloping away from the gap in a direction from the base of the recess toward the surface of member B adjacent the recess. The cover panel has an panel edge nose having a sloping cam follower surface complementary to the cam surface of the frame member. The cam and cam follower surfaces interact upon narrowing of the motion-absorbing gap to apply a force to the cover panel to release the magnet from the magnet striker. The cam surface and cam follower surface are normally spaced apart to enable movements of the cover panel relative to member B upon thermal expansion/contraction of building units of which members A and B are parts.
For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the accompanying drawings.